Measuring Bulk Flow of Galaxy Clusters using Kinematic Sunyaev-Zel'dovich effect: Prediction for Planck

TL;DR

This study predicts how well the Planck satellite can measure galaxy cluster bulk flows using the kinetic Sunyaev-Zel'dovich effect, showing improved accuracy with upcoming cluster catalogs and optimized filtering techniques.

Contribution

It introduces a semi-analytical simulation approach and compares filters, demonstrating enhanced bulk flow measurement accuracy with future cluster data from Planck and eRosita.

Findings

Planck data combined with ROSAT clusters improves bulk flow limits.

Bulk velocity errors decrease with deeper cluster samples.

Unbiased filter reduces systematic bias and improves dipole detection.

Abstract

We predict the performance of the Planck satellite in determining the bulk flow through kinetic Sunyaev-Zeldovich (kSZ) measurements. As velocity tracers, we use ROSAT All-Sky Survey (RASS) clusters as well as expected cluster catalogs from the upcoming missions Planck and eRosita (All-Sky Survey: EASS). We implement a semi-analytical approach to simulate realistic Planck maps as well as Planck and eRosita cluster catalogs. We adopt an unbiased kinetic SZ filter (UF) and matched filter (MF) to maximize the cluster kSZ signal to noise ratio. We find that the use of Planck CMB maps in conjunction with the currently existing ROSAT cluster sample improves current upper limits on the bulk flow determination by a factor \sim 5 (\sim 10) when using the MF (UF). The accuracy of bulk flow measurement increases with the depth and abundance of the cluster sample: for an input bulk velocity of 500 km/s, the UF recovered velocity errors decrease from 94 km/s for RASS, to 73 km/s for Planck and to 24 km/s for EASS; while the systematic bias decreases from 44% for RASS, 5% for Planck, to 0% for EASS. The 95% upper limit for the recovered bulk flow direction \Delta {\alpha} ranges between 4 \circ and 60 \circ depending on cluster sample and adopted filter. The kSZ dipole determination is mainly limited by the effects of thermal SZ (tSZ) emission in all cases but the one of EASS clusters analyzed with the unbiased filter. This fact makes the UF preferable to the MF when analyzing Planck maps.